This invention relates to a sharpness emphasizing method and device used in a picture reproducing machine such as an electronic color separator, for example, a color scanner, a color facsimile, and a color CRT monitor.
In a conventional picture reproducing machine such as an electronic color separator, in order to improve its resolving power or sharpness for reproducing a reproduction picture, an electro-optical unsharp masking or differential masking, or an electronic crisping or peaking has been utilized.
Such methods can improve the resolving power or sharpness to reproduce a sharp or clear reproduction picture. However, these methods have a disadvantage, that is, in these methods, the entire surface of the picture, even a flat portion having little or no detail, is equally improved to be emphasized, and consequently the particles of the original picture are emphasized, resulting in a course reproduction picture.
Recently, in the color separator, a small size film such as a 35 mm size film, is often enlarged up to twenty times in order to reproduce a reproduction picture. In this case, in order to maintain the sharpness of the original picture, the size of a main aperture for obtaining a main signal is reduced depending on the magnification desired of the reproduction picture. Hence, in general, the aperture size is determined approximately to 10 micron.
On the other hand, the size of the particles of the original color picture film is approximately 10 micron, which means that the particles of about 10 micron are distributed even in the flat portion of the original picture film.
Accordingly, when the original picture film is scanned, the level of the main signal obtained is varied by the particles. Further, when the main signal is amplified in a sharpness emphasizing circuit in the color separator, the sharpness emphasizing circuit having a large amplification factor emphasizes the particles of the picture film, with the result of a rough reproduction picture even in the flat portion.
In order to remove such particle influences, conventionally a sharpness emphasizing signal is sliced at a certain fixed slice level, and the uniformly sliced levels of the sharpness emphasizing signal are added to the main signal to emphasize the detail portions of the original picture. However, according to this conventional method, the large detail portions can be sufficiently emphasized, but no small detail portions whose levels are less than the certain slice level, are emphasized at all.